It is well known to form unsaturated chlorinated hydrocarbons by the chlorination of hydrocarbons and partially-chlorinated hydrocarbons. Particularly it is well known to form lower molecular weight chlorinated hydrocarbons, e.g., perchloroethylene, by the vapor phase chlorination of hydrocarbons and chlorohydrocarbons of from 1-3 carbon atoms. For example, trichloroethylene and/or perchloroethylene may be prepared by the chlorination of ethylene dichloride in a fluid bed reactor using as the fluidizing medium various alumina-silica containing materials. Typically these materials comprise a major amount of silica and a minor amount of alumina. The products of this vapor phase chlorination, in addition to trichloroethylene and perchloroethylene, include a number of "light ends", i.e., chlorinated hydrocarbons boiling at a lower temperature than trichloroethylene or perchloroethylene, such as vinylidene chloride; "heavy ends", i.e., chlorinated hydrocarbons boiling at a higher temperature, such as hexachlorobutadiene; large amounts of hydrogen chloride, and small amounts of unreacted chlorine. The gaseous reaction products are then passed into a quench tower wherein the majority of the chlorinated hydrocarbons are converted to the liquid phase while anhydrous hydrogen chloride for the most part remains in the vapor phase and is readily separated. The liquid chlorinated hydrocarbons are then further treated, e.g., neutralized, scrubbed and dried, prior to separation into the desired end product components, trichloroethylene and/or perchloroethylene. This separation is generally accomplished by fractional distillation with the light ends often being recycled to the reactor for further reaction and the heavy ends either recycled for cooling or discarded.
While processes such as the foregoing are reasonably efficient and are in fact in commercial operation, there are certain problems which limit the efficiency and capacity of such plants. Thus, while it is desirable that the trichloroethylene and/or perchloroethylene obtained as final products be of the highest degree of purity possible, the attainment of high purity is complicated by the presence of a number of chlorinated components having boiling points close to the boiling points of trichloroethylene or perchloroethylene. Therefore, in order to obtain the desired purity, fractionating columns containing a large number of plates and operating under a heavy reflux are required. Since a significant portion of the capital investment of a chlorinated solvents plant lies in the cost of the fractionating columns, it would obviously be desirable to eliminate or reduce the formation of those chlorinated hydrocarbons having boiling points close to the boiling points of the intended products. For example, in the fractionation of perchloroethylene (b.p. 121.degree.C.), unsymmetrical tetrachloroethane (U-tet, b.p. 129.degree.C.) and 1,1,2-trichloroethane (b.p. 114.degree.C.) are contaminants which are particularly difficult to remove. Thus, in general, in the production of unsaturated chlorinated hydrocarbons, it would be desirable to prevent the formation of saturated chlorinated hydrocarbons since fractionation would be facilitated and production would be increased (since the saturated hydrocarbons are generally produced by the hydrochlorination of the desired products).
It has now been found that the production of saturated chlorinated hydrocarbons, for example in a process such as described above involving the vapor phase chlorination of hydrocarbons and chlorohydrocarbons in the presence of an alumina-containing material, is caused by hydrochlorination, in the quench tower, of unsaturated hydrocarbons and chlorohydrocarbons, which hydrochlorination is catalyzed by aluminum chloride or active aluminum chloride complexes, generally formed in the reaction tower and carried over in the vapor phase with the gaseous reaction products.